been in the concrete business for 50 years [started out as a...

been in the concrete business for 50 years [started out as a labourer at 14] have had many an argument with engineers as they only have theory to go by never getting their feet wet and actually pleying in the mud ,, i have found that concrete no matter what strenght required has performed better at 90mm /110mm slump than anything under as you have to use to much vibration to get it to flow and combine together ,, also have used steel fibre [at recomendation from an engineer ] found that it balls up and will not mix propoerly through mixes no matter how well concrete is mixed also nearly impossible to pump so anything that can add to strength and workability of concrete is a good thing